1. Field of the Invention
This invention relates to heterocyclic polymers and to methods for their preparation and is more particularly concerned with copolymers of polyparabanic acid and polyamide-imides and with methods for their preparation.
2. Description of the Prior Art
Polyparabanic acids are known in the art; see, for example, U.S. Pat. Nos. 3,609,113 and 3,661,859. These polymers posses excellent thermal stability but, because of their high melting points, are not susceptible of being molded by conventional techniques such as compression molding, extrusion and the like. Accordingly, their use has been limited hitherto to formation of films by casting from solution and to incorporation in coating compositions for wire coating and like applications.
Certain copolymers of polyparabanic acids with other polymers have been described. German Offenlegungsschrift No. 2,404,741 shows the preparation of copolymers which contain parabanic acid and hydantoin moieties. However, these copolymers possess melt characteristics of the same order as the polyparabanic acid homopolymers themselves and are not capable of being molded by conventional techniques other than casting from solutions.
German Offenlegungsschrift No. 2,450,035 shows the preparation of copolymers of parabanic acid and imides but, again, the melt characteristics are such that molding by conventional techniques is not possible.
We have now found that certain copolymers which contain the parabanic acid moiety posses excellent melt characteristics which permit the copolymers to be molded by compression molding techniques and the like. These copolymers also possess the excellent thermal stability and structural strength properties of the polyparabanic acid homopolymers themselves.